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Penetrant Testing 

What is Non-Destructive Testing? 

Non-Destructive Testing (often known by the acronym NDT) is a group of processes used to analyse a material, checking it for defects without causing damage to the item. 

There are two main technologies applicable to NDT – Penetrant Testing (PT) and Magnetic Particle Testing (MT) – and through our value adding supply chain, Silmid are able to supply a wide variety of chemicals and accessories to support both processes. 

Penetrant Testing Process 

The Penetrant Testing Process incorporates 3 product families: Penetrants, Cleaners/Removers and Developers.  


Penetrants are broadly classified into two types, depending on the process used to inspect the component: 

  • Red dye penetrants that are visible against the white of the developer;  
  • Fluorescent penetrants that show any imperfections under ultra violet (UV) light. 

Penetrants can be further classified as to how the surface excess penetrant is removed. 

  • Method A – Water Washable – the penetrant can be removed with water alone; 
  • Method C – Solvent Removable – the penetrant needs to be removed using a solvent based cleaner; 
  • Method D – Post Emulsifiable, Hydropholic – an emulsifier is used to remove the penetrant chemical from the component. 


The cleaner is used to remove excess penetrant from the component, and is sometimes referred to as a remover. There are a number of different cleaning processes available, and this depends on the characteristics of the penetrant used. 


The developer is the final chemical used in the process, and this identifies areas where the penetrant has remained, and therefore reveals any defects in the material or component under testing. 

A brief overview of the process of penetrant testing can be found here, highlighting the differences between Method A, Method C and Method D.